(a) Technical Field
The embodiments of the present invention are directed to a light source driver, and particularly to a light emitting diode (LED) driver.
(b) Discussion of the Related Art
A light emitting diode (“LED”) is used as a light source for various display devices. A cold cathode fluorescent lamp (“CCFL”) is driven by high-frequency AC current, and the LED is driven by DC current.
A DC/DC converter used for driving the LED includes a rectifier circuit unit for generating a DC current. An LED driving method for controlling luminance of an LED includes a pulse width modulation (“PWM”) dimming control method and an analog dimming control method. The PWM dimming control method controls brightness of the LED by adjusting an on/off duration ratio of the LED depending on a PWM signal. For example, when a PWM signal provided to the LED has an on/off duration ratio of 4:1, the brightness of the LED reaches 80% of the maximum brightness. The analog dimming control method controls brightness of the LED by adjusting the current supplied to the LED.
An LED driver drives a bipolar junction transistor (“BJT”) or a metal-oxide-semiconductor field-effect transistor (“MOSFET”) in a linear region to control impedance between the collector and emitter and to keep the current flowing through the LED constant.
The BJT or the MOSFET is used as a current regulator for constantly maintaining the current flowing across a light source. The current regulator enables current to stop flowing through the LED when PWM dimming is turned off to prevent deterioration of characteristics of the light source, which may result in a voltage stress to the current regulator.